There have been conventionally inkjet recording devices which form images on recording media by ejecting ink from a plurality of nozzle openings. In the inkjet recording devices, an increasing number of nozzle openings have been arranged in high density in accordance with improvement of accuracy of the formed images.
In order to achieve faster image formation, the inkjet recording devices are provided with a plurality of inkjet heads (nozzle units) arranged in parallel to form a wide range of images at once. When the interval of nozzle openings in a width direction is narrowed in accordance with the improvement of accuracy, it is difficult to arrange the nozzle openings in a single row. Thus, there has been used a technique of providing the nozzle openings in high density in the width direction as a whole by arranging the nozzle openings so as to be dispersed in a plurality of rows in the conveyance direction. In order to prevent the plurality of inkjet heads from occupying large space, Patent document 1 discloses a technique in which a plurality of print head subunits (head chips, recording heads) is attached to a structure rod material in a staggered manner. The Patent documents 2 and 3 disclose techniques which shorten the width in the conveyance direction of a recording medium by forming head units arranged in such staggered manner in a nearly trapezoidal shape and alternately arranging the head units.
The position accuracy in attaching the inkjet heads has been important for image accuracy in accordance with the increase in density of nozzle openings arrangement. The position accuracy includes relative position accuracy between a plurality of inkjet heads. Thus, there has been recently a technique of accurately attaching head chips of inkjet heads to head modules by using an optical measuring scope or such like.